1. Field of the Invention
The present invention relates to an image forming apparatus, control method thereof and computer-readable storage medium.
2. Description of the Related Art
As information technology becomes prevalent in offices, security is becoming a big concern. Leakage of digital confidential information can be prevented by access restriction and the like. However, when confidential information is printed on paper by an image forming apparatus or the like, it is difficult to check or inhibit printed paper from being carried out.
As a measure against this, a system is proposed that prints security information such as a digital watermark or QR code on paper. Even if paper-based information leakage occurs, this system extracts security information from the leaked paper, specifying a user and apparatus that printed the paper. A system of this type is proposed in, for example, Japanese Patent Laid-Open No. 2003-280469.
However, the conventional technique suffers the following problem. For example, when a QR code is printed as security information, it is printed only on part of the paper. If only an area of the paper where the QR code is not printed is scanned and copied, the QR code is not printed.